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Don't warn about returning Any if it is a proper subtype of the return type #3473

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May 30, 2017
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3 changes: 2 additions & 1 deletion mypy/checker.py
Original file line number Diff line number Diff line change
Expand Up @@ -1874,7 +1874,8 @@ def check_return_stmt(self, s: ReturnStmt) -> None:
if isinstance(typ, AnyType):
# (Unless you asked to be warned in that case, and the
# function is not declared to return Any)
if not isinstance(return_type, AnyType) and self.options.warn_return_any:
if (not is_proper_subtype(AnyType(), return_type) and
self.options.warn_return_any):
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I would have tested for the option first, an attribute access is cheaper than a call. It's a reflexive optimization that often also leads to clearer code (often it's a wash).

self.warn(messages.RETURN_ANY.format(return_type), s)
return

Expand Down
17 changes: 17 additions & 0 deletions test-data/unit/check-warnings.test
Original file line number Diff line number Diff line change
Expand Up @@ -165,3 +165,20 @@ from typing import Any
def g() -> Any: pass
def f() -> Any: return g()
[out]

[case testOKReturnAnyIfProperSubtype]
# flags: --warn-return-any --strict-optional
from typing import Any, Optional

class Test(object):

def __init__(self) -> None:
self.attr = "foo" # type: Any

def foo(self, do_it: bool) -> Optional[Any]:
if do_it:
return self.attr # Should not warn here
else:
return None
[builtins fixtures/list.pyi]
[out]